AMD "Southern Islands" GPU

It's always exciting to see AMD or NVIDIA come out with a completely new GPU architecture. The "Southern Islands" GPUs are AMD's implementation of its "Graphics Core Next" architecture, and comprise three different families of GPUs:

Tahiti for high-end cards like the Radeon 7970 and 7950

Pitcairn for more mainstream users

Cape Verde brings up the low end

AMD made the Tahiti-based Radeon 7970 and 7950 cards available first, followed now by the Cape Verde-based 7770 and 7750. Pitcairn cards are as yet unavailable.

Graphics Core Next

AMD had several goals in mind for Graphics Core Next, and one of the main things they wanted to do was to catch up with NVIDIA in the "GPU compute" arena. Right now, NVIDIA's "CUDA" (Compute Unified Device Architecture) dominates in GPU computing, with a robust set of developer tools and years of track record behind it. AMD's "DirectCompute" alternative has been around almost as long but has failed to catch on with developers to the degree that CUDA has. AMD is making a real push for DirectCompute with these new GPUs, and claims that over 200 applications already benefit from DirectCompute technology.

For Southern Islands, AMD has grouped simple ALUs (arithmetic logic units) into a single SIMD (Single Instruction Multiple Data) unit. A number of SIMD units, along with instruction decoders and schedulers, branch units, vector processors, and other items comprise a compute unit, and a number of these compute units (along with memory controllers and whatnot) comprise a Southern Islands GPU chip. Each compute unit comprises 64 shaders; the 7970 has the full complement of 32 compute units (and thus 2,048 shaders), the 7950 has 28 compute units (1,792 shaders), while the Radeon 7770 has 10 compute units (640 shaders). The Cape Verde GPU has about 1.5 billion transistors as compared to Tahiti's 4.3 billion.

Here's a summary of the specifications of the XFX cards Benchmark Reviews has tested so far:

# shaders

Stock Shader Clock

XFX Shader Clock

Stock memory clock

XFX Memory Clock

Memory

Memory Interface

Power

XFX R7970

2,048

925MHz

1000MHz

1375MHz

1425MHz

3GB

384-bit

8-pin & 6-pin

XFX R7950

1,792

800MHz

900MHz

1250MHz

1375MHz

3GB

384-bit

Two 6-pin

XFX R7770

640

1000MHz

1120MHz

1125MHz

1300MHz

1GB

128-bit

One 6-pin

AMD has tweaked their VLIW (very long instruction word) architecture to provide more consistent performance. Previous generations of AMD GPUs often left many compute units/stream processors idle, because dependencies in the data being worked on meant that not all the compute units could be used at once. Southern Islands architecture provides a greater degree of parallelism (it's that SIMD stuff, really, being used effectively) and can keep most compute units working all the time, leading to more consistent (and higher) performance. This has obvious advantages in both graphics processing and general GPU-compute operations.

Other enhancements common to all of AMD's new GPUs include:

Partially Resident Textures: As games increasingly use very large textures, loading and manipulating the texture data takes more time. A Southern Islands GPU can load only the part of the texture that will actually be visible in a frame, reducing the memory bandwidth and workload.

Error-correcting code support: There's not much detail on this feature yet, but it looks as if AMD will be able to offer optional ECC support (important for industrial applications) without having to use ECC memory. This will detect and correct memory errors, although AMD's tech white paper doesn't go into specifics such as how many bits can be detected/corrected.

PowerTune and ZeroPower: These feature dynamically clock the card's GPU and memory doesn (PowerTune) when high performance isn't needed, and can shut off entire sections of the GPU (ZeroPower) when the card is idle. For example, the second card in a CrossFireX system can be idled down to less than 5 watts if you're just browsing the Windows desktop; a single card system will power down if your display goes to sleep. Combined with the inherent efficiency of the 28nm fabrication process, this results in significant power savings. Side benefits you'll notice include less heat and noise emanating from your rig, especially when you're not gaming.

Eyefinity 2.0: New support for 5x1 monitor layouts, improved bezel correction, and support for custom resolutions enhance AMD's existing Eyefinity feature. I saw a 5x1 system demonstrated at an AMD press even a few months ago and it was quite impressive.

28nm fabrication process: If you make 'em smaller, you can fit more of 'em in. The 7970 GPU has a staggering 4.3 billion transistors, and even the 7770 has 1.5 billion. The original Intel 4004 microprocessor had about 2,300. My 1969-vintage HP 9100B programmable calculator has 40.

PCI Express 3.0 support: This has twice the bandwidth of PCI-E 2.0, but I'm not sure what real-world effect this will have, especially on x16 slots. Even the beefiest current video cards aren't hobbled by 8x PCI-E 2.0 bandwidth.

Let's take a look at what these features actually mean on a real, live video card.

I might be wrong, but I did not see if this card allows control of the vCore. This is a must have option IMHO. Not all cards allow this. For Example, the VisionTek 6850's are not able to up the voltage. Not even flashing the BIOS with a custom profile will work.

Right now the various hacking tools (MSI Afterburner) for the AMD GCN graphics cards are in a pretty primitive state. I wasn't able to get voltage control working for the 7970 and 7950 cards, and didn't even try with the 7770. I'm sure this will change in the future, though.

I don't understand why bmr keeps giving AMD cards a negative because they have no physx. It's not like they even have a choice since physx is proprietary. It's like holding nVidia cards responsible because they don't support eyefinity. I respect your opinion on including this, I just would be interested why you choose to include that.

According to NVIDIA, PhysX is an open standard anyone can write to. They were saying this as early as 2008. There are doubtless behind-the-scenes reasons nobody else has implemented it; and there are competing physics engines like Havok and Bullet, but it all begs the point: it's a significant advantage to NVIDIA cards since so many games use it. Your Eyefinity example isn't a good one since NVIDIA provides equivalent functionality with their "Surround" feature. I tend not to weight either of these too heavily since only a tiny fraction of users run triple monitor setups.

I know you don't push it too much which I appreciate because there are enough people that don't understand what it means exactly. I don't begrudge nVidia for owning physx but as far as I know it will only run on nVidia hardware. Sure, the software may be open for development but if it isn't able to run on anything but nVidia cards doesn't that make it being an open standard kind of pointless? As for the eyefinity example. I realize it's not the clearest example but my point was that it's an AMD technology that nVidia doesn't have. You bring up that nVidia has surround however surround isn't exactly equivalent considering anything I can find about says it supports a max of three monitors whereas eyefinity supports 6. I'm not saying one or the other is better just that they're different in functionality. I can see your point though and the more I think about it, the more I see the reason for including physx. I just haven't seen it come up as a topic on here before. It would be interesting to see a review on physx, not in pure numbers but rather simply did it look/feel much better with physx? Hey, maybe with enough pressure AMD would pick it up and use it. I can dream huh?

How much of a difference PhysX makes depends of course on how well the developer uses it in a game. Probably the best showcases for the technology are the Batman: Arkham Asylum and Arkham City titles. The games are perfectly playable without PhysX but it really adds to the atmosphere when it's enabled.

You're right about Surround being limited to 3 monitors, which is probably why AMD has been showing off 5-monitor setups of late. I know one or two people with triple monitor setups, but the only 5-monitor setup I've ever seen was an an AMD press event. Impressive, yes; real-world utility, well...

Well I like the battle that's shaping up with this gen of cards. nVidia has their advantages, AMD has theirs (primarily first strike). I just hope nVidia punches back hard enough that they force AMD to drop prices. This HD 7770 would be just what I need to replace the 8800GT that recently died in my spare computer. Unless you know something about the next nVidia cards you'd like to share ;)

I like the looks of this card. It's striking. But the price turns all of that off immediately. If the price were to fall a ~good~ bit, I could see running a pair of them in my A8-3850 Vision PC. The low power usage and lower heat appeal to me.